Alcohol is eliminated from the body by two mechanisms: metabolism and excretion. Metabolism accounts for the removal of greater than 90% of the alcohol consumed, removing it from the body via oxidation of the ethyl alcohol molecule to carbon dioxide and water primarily in the liver. The remaining alcohol is excreted unchanged wherever water is removed from the body, breath, urine, perspiration, and saliva.
Although excretion accounts for less than 10% of the eliminated alcohol, it is significant because unaltered alcohol excretion permits an accurate measurement of alcohol concentration in the body by way of both breath analysis and insensible skin perspiration. Insensible skin perspiration is the vapor that escapes through the skin through sweating. This insensible skin perspiration can be used to obtain a transdermal measurement estimating a measure of blood alcohol concentration (BAC), referred to as transdermal alcohol concentration (TAC).
A survey of literature reveals that there are no reports available for continuously monitoring TAC through transdermal diffusion or perspiration, because the pharmacokinetic process of alcohol is complex owing to the intricate nature of its distribution into the various tissues of the body. The balance between absorption and elimination of alcohol is reflected in the BAC, which continues to rise until absorption is complete. After a maximum value is reached, the BAC begins to decrease during the elimination phase primarily due to the metabolism process in the liver as well as through transdermal diffusion.
A number of ethanol sensors have been developed for monitoring driving under the influence (DUI) offenders. The types of ethanol sensors include, for example, spectrophotometers, semiconductor sensors, and fuel cell sensors. Among these, the principle behind spectroscopic sensors involves the measurement of changes in light wavelength and intensity in the presence of ethanol. The semiconductor sensor monitors changes in resistance due to changes in ethanol concentration. The fuel cell sensor monitors the oxidation of ethanol at the anode while reducing the atmospheric oxygen at the cathode. The fuel cell sensor has high specificity, accuracy, calibration stability and long working life compared to the other two types of sensors. However, these sensors all suffer from high interference caused by humidity and cannot be used for continuous monitoring. One example of a widely used ethanol sensor is the breathalyzer, which is incapable of continuously monitoring ethanol concentration in DUI offenders.
Therefore, there still remains a need for stable and selective ethanol sensors that are effective in a humid environment.